Metallic microlattice

Metallic microlattice is an ultra-light, highly porous metallic material composed of a three-dimensional network of interconnected struts or beams arranged in a periodic lattice structure. Despite being made of metals, these microlattices exhibit extremely low density, high elasticity, and remarkable strength-to-weight ratios. They are often described as the lightest structural materials ever created, combining the mechanical robustness of metals with the lightness of foams or aerogels.
Developed through advances in materials science, nanotechnology, and additive manufacturing, metallic microlattices have a broad range of applications in aerospace engineering, energy absorption, and next-generation lightweight structures.

Discovery and Development

The first metallic microlattice was developed in 2011 by a team of researchers from HRL Laboratories, Boeing Company, and the California Institute of Technology (Caltech). The material gained global attention when it was described as “100 times lighter than Styrofoam” and capable of balancing on a dandelion fluff without damaging it.
This groundbreaking innovation resulted from ongoing research into architected materials—engineered structures that derive their properties from controlled geometry rather than composition alone. By fabricating materials with highly ordered, open-cell structures, scientists achieved extraordinary combinations of strength, elasticity, and density.

Structure and Composition

Metallic microlattices are composed of hollow metallic tubes or solid struts arranged in a repeating geometric pattern. The lattice architecture typically consists of octahedral, cubic, or tetrahedral units, which distribute stress evenly throughout the structure.
Key structural characteristics include:

• Porosity: 99.9% air by volume.
• Density: As low as 0.9 milligrams per cubic centimetre, making it lighter than aerogel and nearly comparable to air.
• Material composition: Commonly made of nickel, nickel-phosphorus, aluminium, titanium, or other metal alloys, depending on application requirements.

The mechanical properties of the microlattice stem from both the geometry of the lattice and the properties of the base metal.

Fabrication Techniques

The fabrication of metallic microlattices relies on advanced microfabrication and metallisation methods that allow precise control of architecture at the microscopic scale.
The typical process involves several steps:

1. Polymer Template Formation: A three-dimensional polymer lattice is created using photolithography, laser writing, or 3D printing techniques such as stereolithography.
2. Metal Coating (Electroless Plating): The polymer template is coated with a thin layer of metal (e.g., nickel-phosphorus) using electroless deposition or chemical vapour deposition (CVD).
3. Template Removal: The polymer scaffold is dissolved or burned away, leaving behind a hollow metallic lattice with ultra-thin struts.
4. Post-Processing: The structure may undergo heat treatment or coating to improve strength, conductivity, or corrosion resistance.

This process enables precise control over lattice geometry, strut thickness, and metal composition, allowing scientists to tailor properties for specific engineering needs.

Mechanical Properties

Metallic microlattices exhibit an extraordinary combination of mechanical resilience, low density, and energy absorption.
Key properties include:

• Ultra-lightweight: Some microlattices weigh less than 1 milligram per cubic centimetre, nearly 100 times lighter than conventional metallic foams.
• High Elasticity: They can compress up to 50% of their height and recover fully, demonstrating superelastic behaviour.
• Strength-to-Weight Ratio: Despite their lightness, they retain high structural strength relative to their mass.
• Energy Absorption: Excellent at dissipating mechanical energy, making them ideal for impact protection.
• Thermal Conductivity and Electrical Conductivity: Retain metallic characteristics depending on composition.

The combination of low density and recoverability distinguishes metallic microlattices from other lightweight materials like aerogels and polymer foams.

Comparison with Other Lightweight Materials

Metallic microlattices thus occupy a unique position among ultra-lightweight, high-performance materials, combining the mechanical and conductive advantages of metals with the architecture-driven resilience of cellular materials.

Applications

The potential applications of metallic microlattices span numerous industries, particularly those requiring lightweight yet strong materials.
1. Aerospace and Defence:

• Used in lightweight structural components to reduce fuel consumption.
• Potential for impact absorption and vibration damping in aircraft and spacecraft.
• Serves as a core material in sandwich panels for spacecraft structures.

2. Automotive Industry:

• Acts as a crash energy absorber in safety systems.
• Enables lighter vehicles with improved fuel efficiency.

3. Thermal and Acoustic Insulation:

• High porosity makes it effective for thermal management and sound absorption.

4. Battery and Energy Applications:

• Serves as a lightweight current collector in batteries or as an electrode support in fuel cells.
• Offers large surface area for electrocatalytic reactions.

5. Biomedical Engineering:

• Possible use in bone scaffolds or implants, where low weight and structural porosity facilitate tissue integration.

6. Protective Equipment:

• Used in shock-absorbing panels, helmet liners, and blast protection systems due to its exceptional energy absorption capacity.

Scientific and Engineering Significance

The development of metallic microlattices marks a major advance in the field of architected materials. Traditional materials derive their properties from composition; however, microlattices derive them from geometry and scale. This paradigm allows for the creation of materials that can be tuned for specific mechanical or thermal behaviours without altering the base metal.
Metallic microlattices have contributed to the study of:

• Mechanical metamaterials, which exhibit unusual behaviours like negative Poisson’s ratio (auxetic properties).
• Energy dissipation mechanics, crucial for aerospace safety.
• Micro-architectural optimisation, using computational design to achieve maximum performance at minimum weight.

Recent Developments

Since the original nickel-phosphorus microlattice, research has expanded to develop new variants and fabrication methods:

• Titanium and aluminium microlattices for higher temperature stability.
• 3D-printed microlattices with tunable pore geometries.
• Hybrid microlattices, combining metallic and polymer components for multifunctional performance.
• Integration with nano-coatings for corrosion resistance and conductivity enhancement.

In recent years, NASA, Boeing, and other aerospace organisations have tested metallic microlattices for use in satellite components and spacecraft shielding, given their combination of lightness and mechanical stability.

Environmental and Economic Perspectives

While fabrication of metallic microlattices involves high-precision manufacturing and can be costly, their long-term benefits in weight reduction, fuel efficiency, and material recyclability make them economically and environmentally favourable for high-performance industries.
Ongoing research focuses on scalable, cost-effective manufacturing, potentially through additive manufacturing (3D printing) and automated electroless plating, enabling broader industrial application.